Land transportation vehicles such as, for example, railway trains and trucks are provided with suitable suspension devices made by laminating together a plurality of leaf springs 10 as shown in FIG. 7. Each leaf spring 10 is made from a rolled material with a necessary thickness which is, after the process of forming an eye at one or both ends of a plate material, or tapering the other end thereof, given a necessary "deflection," or camber, during the state wherein the whole material is heated. There are various types of cambers: the curvature gradually reduces or increases from the center toward both ends; the central part is formed flat, and the like, depending upon the use or load stress applied.
FIG. 8 illustrates an example of a prior art apparatus 12 for cambering leaf springs 10. The apparatus 12 basically consists of an upper mold 14 and a lower mold 16, and the upper mold 14 has a female or concave shape, while the lower mold 16 has a male or convex shape. A leaf spring 10 immediately after being heated to the hot process temperature is inserted between the upper mold 14 and the lower mold 16, and then the upper mold 14 is forced to approach the lower mold 16 so as to impart to the plate 10 the camber in accordance with the surface shape of the molds 14 and 16. This cambered leaf spring 10 is then tempered by immersing it within a tempering oil contained within an oil tank.
In accordance with the foregoing, there is a serious problem that if such cambered leaf spring 10 is immersed within the oil without any constraint for the leaf spring 10 while carrying out the tempering thereof, it is distorted during the cooling process. A countermeasure for such has been proposed by means of which the cambered leaf spring 10 is constrained as it is, and immersed within the oil in this state so as to prevent the distortion which may occur during the cooling process.
For example, the distortion preventive means shown in FIG. 9 comprises a plurality of movable claw members 22 provided upon a conveyor 20 which is movable within an oil tank 18 and which are designed to mechanically hold the leaf spring elements 10 at strategic positions. Namely, the leaf spring 10 to which the required camber has been given by means of the cambering apparatus 12 is held by means of the group of claws 22 located at the entrance side of the oil tank 18, and the conveyor 20 is then circulated with the leaf springs 10 held thereon thereby immersing them within the oil so as to carry out the tempering thereof.
The distortion preventive means shown in FIG. 10 rotatably supports therein an octagonally shaped main body 24. The main body 24 has cambering apparatus 12 mounted upon each surface thereof and the lower part of the main body 24 is designed to be immersed within the oil contained within the oil tank 18. A heated straight leaf spring element or member 10 is loaded upon the cambering apparatus 12 at a position located above the oil level and held between the upper mold 14 and the lower mold 16 so as to carry out the cambering thereof. Then, the main body 24 is rotated in the above state so as to immerse the cambered leaf spring 10 within the oil contained within the oil tank 18 as the spring element 10 is held between the upper mold 14 and the lower mold 16.
Furthermore, in accordance with the distortion preventive means shown in FIG. 11, each leaf spring element 10 is cambered by pressing it between an upper mold 14 and a lower mold 16 of the cambering apparatus 12, and then the cambering apparatus 12 is immersed within the oil contained within an oil tank 18. The cambering apparatus 12 is moved within the oil tank 18 by an appropriate carrying means so as to carry out tempering of each cambered leaf spring 10 loaded within the cambering apparatus 12. After the cambering apparatus 12 is removed from the oil tank 18, the upper mold 14 and the lower mold 16 are separated from each other so as to remove the tempered leaf spring 10. Still further, the distortion preventive means shown in FIG. 12 comprises a single cambering apparatus 12 which is designed to hold the plate spring 10 tightly between the upper mold 14 and the lower mold 16 and to immerse the thus held leaf spring 10 within the oil tank 18. The oil tank 18 is pivoted by means of an appropriate pivoting means so that the leaf spring 10 held by means of the cambering apparatus 12 may be properly tempered.
For manufacturing such cambered leaf springs 10, there are two kinds of methods: 1 to effect cambering of leaf springs 10 of the same shape and specification continuously within a group or by means of group processing (the industry calls this method "Group making"), and 2 a family of leaf springs 10 comprising the main leaf spring 10 and the smaller leaf springs 10 constituting a suspension device are cambered together (the industry calls this method "Family making"). It depends upon the users' choice considering the application and other factors as to which method is used for cambering the leaf springs. In the Group making method, a required number of leaf springs of the same shape are cambered together, and only when the shape of the camber is changed, the upper mold 14 and the lower mold 16 of the cambering apparatus 12 are replaced. The systematic processing for replacing these molds usually requires a considerable amount of time, which has been a major factor significantly lowering the efficiency in connection with the leaf spring cambering work. Especially today when small lot production is pervasive, makers are required to respond to frequent order changes within such production system, and consequently, the reduction of the setup time required for the replacement of the molds is a highly important concern within the industry.
Furthermore, in accordance with the Family making method, the family of leaves comprises leaf members having slightly different cambers, so that the upper mold 14 and the lower mold 16 have to be replaced each time one of the leaves 10 is cambered. Therefore, the latter method involves extremely troublesome replacement work and increased loss of production time. The conventional cambering systems have therefore failed to meet the needs of the industry in this respect. Whether the Group making method or the Family making method is employed, many kinds of upper molds 14 and lower molds 16 corresponding to a variety of camber size requirements are necessary, leading to a great increase in production costs. Moreover, these molds have to be stored in groups of the same type, requiring an enormous storage space, and therefore giving rise to problems wherein their storage and maintenance becomes quite complex.
From another viewpoint, the following problems have also been encountered in connection with those proposed methods for preventing distortions suffered by means of the leaf springs 10 when they are subjected to the tempering process subsequent to the cambering process.
Namely, in the method described in connection with reference to FIG. 9, although the degree of distortion can be reduced as compared with the case when the leaf spring 10 is not constrained, distortion still occurs at the unconstrained portions since leaf spring 10 is not entirely constrained by only partly constrained at predetermined locations thereof. In the method described in connection with reference to FIG. 10, the cambered leaf spring 10 is immersed within the oil as it is entirely constrained within the cambering apparatus, so that the occurrence of distortion can in fact be prevented. However, such distortion prevention system tends to be complicated in structure and expensive. In this method, since the main body 24 rotates, the leaf springs 10 are immersed within the oil in an inclined state, which may cause another problem that a different kind of distortion is liable to be caused within the leaf spring which is different from the ones caused by means of the other methods described above.
The method described and illustrated in connection with FIG. 12 has the merit of minimizing distortion as compared with the methods shown in FIGS. 9 through 11, but suffers the disadvantage of extremely low productivity. Furthermore, the methods shown in FIGS. 9 through 12 involve such common disadvantages in that they require very troublesome work including adjustment of the claw members 22 for properly constraining the leaf springs 10 and for replacing the molds 14 and 16 according to the order changes for a particular leaf spring 10, and obviously such setup procedures require much time. Moreover, the methods described in connection with and illustrated within FIGS. 9 through 12 also suffer problems that, since the cambering apparatus 12 itself is immersed within the oil for carrying out the tempering of the leaf springs, a plurality of molds 14 and 16 corresponding to the respective camber specifications have to be prepared, leading to increased production costs.